Valentino Rossi was quickest in Friday practice for the Spanish Grand Prix at Jerez.
Yamaha's world champion beat Loris Capirossi to the top spot by 0.364 seconds, with Casey Stoner 0.621s down on his title rival in third.
Stoner had briefly been fastest in the early moments of the session, before the Ducati rider was deposed by Rossi.
Yamaha then established a one-two-three sweep for much of the afternoon, with Rossi ahead of his factory squad team-mate and championship leader Jorge Lorenzo, and Tech 3's Colin Edwards moved up to third.
As the session neared its end, Stoner edged back up to second place, but he would loose this spot in the closing minutes as Capirossi buoyed Suzuki by grabbing second and ending the day as Rossi's closest challenger.
Lorenzo remained fourth, with Edwards falling to sixth at the end as Honda's Andrea Dovizioso improved.
LCR Honda's Randy de Puniet took a promising seventh, ahead of Chris Vermeulen on the second Suzuki.
Marco Melandri again impressed for Hayate Kawasaki by beating last year's Jerez winner Dani Pedrosa (Honda) to ninth.
It was another poor session for Stoner's team-mate Nicky Hayden. The former champion continued to struggle with the factory Ducati and was back in 17th place, 2.3s off the pace.
Pos Rider Bike Time Gap
1. Valentino Rossi Yamaha 1m39.647s
2. Loris Capirossi Suzuki 1m40.011s + 0.364s
3. Casey Stoner Ducati 1m40.268s + 0.621s
4. Jorge Lorenzo Yamaha 1m40.441s + 0.794s
5. Andrea Dovizioso Honda 1m40.601s + 0.954s
6. Colin Edwards Tech 3 Yamaha 1m40.703s + 1.056s
7. Randy de Puniet LCR Honda 1m40.866s + 1.219s
8. Chris Vermeulen Suzuki 1m41.063s + 1.416s
9. Marco Melandri Hayate Kawasaki 1m41.182s + 1.535s
10. Dani Pedrosa Honda 1m41.208s + 1.561s
11. James Toseland Tech 3 Yamaha 1m41.461s + 1.814s
12. Sete Gibernau Hernando Ducati 1m41.531s + 1.884s
13. Alex de Angelis Gresini Honda 1m41.557s + 1.910s
14. Mika Kallio Pramac Ducati 1m41.584s + 1.937s
15. Toni Elias Gresini Honda 1m41.736s + 2.089s
16. Yuki Takahashi Scot Honda 1m41.898s + 2.251s
17. Nicky Hayden Ducati 1m41.916s + 2.269s
18. Niccolo Canepa Pramac Ducati 1m42.063s + 2.416s